"the doctrine of opposition to the separation of church and state."
An unfortunately common stance in the US, especially given that many of the early colonies were founded, by various groups, to escape religious persecution.
In case it’s not obvious, by the way, I’m in a political mood today, and I’m sitting on a train bored.
Anyway, my primary reason for being in favour for the total separation of Church and State is that it inevitably leads to discrimination, in several ways.
In the UK, "the Church" is generally the Church of England. Now, if the government allows its policies to be dictated by the Church of England, and if it governs the country in a way that would be appropriate with the CoE as "The Church", it’s going to lead to conflict. There are very few points that every religion with more than a trivial representation in the UK will agree on; making any kind of religious doctrine into law will alienate religions that disagree with that doctrine (for the purposes of this discussion, I’m considering atheism to be a religion, whose supporters disagree with every religious doctrine out of sheer bloodymindedness if nothing else).
The other problem is that many religious doctrines are discriminatory in themselves. The obvious one is the Christian insistence that "I am the Lord your God; you will have no other God before me". Insisting that other religions are inherently sinful tends to piss them off a bit.
Another, which is currently an issue in the US, is the opposition to homosexuality in general, and gay marriage in particular. Basically, the main argument seems to be "it’s un-Christian", which would be a perfectly acceptable argument in a Christian country and is therefore a perfect reason why there should not be such a thing as "a Christian country" (or any other religion, for that matter). It is simply not acceptable to discriminate against any group simply because some other group claims that the first group is sinful, especially based on the frankly pretty shaky evidence that Christianity has. In the UK, it appears that it’s allowable for gay people to have all the benefits of marriage as long as they don’t call it marriage; frankly, if the Church of England are that petty they need to grow up, and they certainly shouldn’t be given any say in national policy.
Apparently, the Italian government recently voted against a law that would make it illegal to discriminate against gay people, under pressure from the Vatican (who presumably didn’t want to get sued). It’s a little worrying that Italy worries so much about what another country thinks.